Note: Descriptions are shown in the official language in which they were submitted.
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ME T HOD AND SYSTEM FOR DIRECTIONAL DRILLING AND COUPLING
SUB
The invention relates to a method and system for
directional drilling and to a coupling sub suitable for
the system. The drilling system may be an abrasive jet
drilling system. The method and system may be applied for
drilling wellbores for the production of hydrocarbons.
An abrasive jet drilling system may comprise a
rotatable drill string and a drill bit connected to a
downhole end of the drill string. Said drill bit may
comprise at least one jet nozzle for generating one or
more jets of a mixture of drilling fluid and abrasive
particles. The drill string is provided with a fluid
passage for transferring the drilling fluid from an
uphole end at surface to the drill bit.
Such drilling system is for instance disclosed in WO-
2005/005767. The jet drilling system of WO-2005/005767
may be introduced in a borehole to erode to bottom
thereof using the one or more abrasive jets, which are
discharged from the jet nozzle. The abrasive particles
may be circulated in the drilling system and may be
introduced in the drill string mixed in the drilling
fluid. Alternatively, the abrasive particles may be
recycled using a downhole recycling device. Herein, less
particles have to travel back and forth to surface,
saving costs and improving efficiency.
The abrasive jet drilling system can produce both
straight and curved boreholes. However, conventional
steering techniques are generally unsuitable for the jet
drilling system. For instance, abrasive jet drilling
requires a relatively high drilling fluid pressure for
the abrasive jet. In addition, abrasive jet drilling may
obviate the requirement to apply weight on the drill bit
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(weight-on-bit (WOB)) or torque to the drill string as in
conventional drilling systems.
The absence of weight on bit allows the application
of flexibility in the drill string or the drilling
assembly, enabling the drilling of curved sections having
a relatively small radius. However, when drilling a
straight section of the wellbore, the drill string and
the drilling assembly are preferably relatively stiff. A
stiff drilling assembly is more suitable to maintain a
straight drilling direction, as a stiff drilling assembly
has less or even no freedom of movement to deviate from a
straight line. In contrast, a flexible drilling assembly
would be better suited to drill in any desired direction,
and would therefore be preferred for curved sections of
the wellbore.
The present invention aims to provide an improved
abrasive jet drilling system which is fit for both the
drilling of straight sections and for directional
drilling.
The invention therefore provides a coupling sub for
coupling a first drill string section to a second drill
string section in a directional drilling system, the
coupling sub comprising:
- a first end connectable to the first drill string
section;
- a second end connectable to the second drill string
section;
- a hinge member between the first end and the
section end allowing hinging of the second end relative
to the first end; and
- locking means, operable between a hinge mode and a
locking mode for locking the hinge member to prevent
hinging of the second end relative to the first end.
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The coupling sub is suitable to be included in a
drill string comprising at least two adjoining drill
string sections. The coupling sub connects said drill
string section to each other and allows rotation of the
drill string sections with respect to each other
according to rotational axes which are oriented
transversely with respect to the longitudinal direction
of the drill string. The locking means have a locking
mode for locking the drill string sections in aligned
position and a free mode for allowing rotation of the
drill bit parts with respect to each other. Herein, the
hinge member transfers torque from the first drill string
section to the second drill string section both in the
hinge mode and in the locking mode. In the locking mode,
the drill string sections are axially aligned. In the
hinge mode, the hinge member allows the axis of the
second drill string section to make an angle with respect
to the axis of the first drill string section. The
coupling sub functions for instance as a universal joint
which can be locked in an aligned arrangement. In an
embodiment, said angle between the first and second drill
string sections may be in the range of about 2 to 20
degrees, for instance about 5 to 10 degrees.
The coupling sub according to the invention may be
integrated in the drill string or in the drilling
assembly, allowing the latter to be transferred between
two modes. When drilling a straight borehole section, the
drill string sections are locked in aligned relation with
respect to each other. When drilling a curved section of
the borehole the drill string sections are unlocked
allowing the hinge member to hinge. This increases the
flexibility of the drill string, allowing the drill
string to follow a curved trajectory. In the hinge mode
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the drill string can bend in the direction of, or
against, the borehole wall. Herein the angle between the
axis of the drill bit and the axis of the borehole will
change. Said angle changes substantially proportionally
to the angle between the first and second drill string
sections. As a result the bottom of the borehole will be
eroded unevenly, creating an angle with respect to the
borehole axis. The drilling system enables the drill bit
to follow that angle and change the drilling direction.
In an embodiment, the coupling sub of the invention
is included in a
The flexibility of the drill string can be obtained
in different ways. According to a first possibility the
coupling means comprise spring means, such as coaxial
coil springs with opposite winding directions. According
to another possibility, the coupling means comprise a
universal joint.
In all those embodiments, the drill string parts each
have a through going channel part, said through going
channel parts being connected to each other through a
flexible conduit which extends through the coupling
means. By means of said flexible conduit, the flow of
fluid, together with abrasive particles contained
therein, can be reliably transferred through the flexible
part of the drill string.
The locking means can be carried out in various ways
as well. According to a preferred embodiment, the
locking means comprise a locking sleeve which is carried
by one of the drill string parts in such a way that said
locking sleeve is translatable according to the
longitudinal direction of said drill string part, said
locking sleeve and the other drill string part comprising
facing locking surfaces, whereby in the retracted
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position of the locking sleeve said locking surfaces are
at the distance from each other and the drill string
parts are rotatable with respect to each other and in the
extended position said facing surfaces engage each other
so as to prevent mutual rotations of the drill string
parts. The mating locking surfaces are preferably
carried out in such a way that a firm connection is
obtained between the drill string parts. Preferably
therefore, the mating surfaces are cone shaped.
Furthermore, the drill string part which carries the
locking sleeve may comprise an actuator for displacing
said locking sleeve. Preferably, the circumference of the
drill string part which carries the locking sleeve and
the circumference of the locking sleeve are sealed with
respect to each other. Such sealing prevents the entry of
cuttings and the like in the drill string. Furthermore,
for this purpose the drill string part which carries the
locking sleeve may be provided with a fixed blocking ring
which surrounds the locking sleeve, a seal being provided
between said blocking ring and the other drill string
part.
Preferably a coupling sub is provided comprising the
drill string sections, the hinge means and the locking
means, said coupling sub being connected to and
positioned between the drill string and the drill bit.
One or more coupling subs can be included in the drill
string at any desired position along the drill string. In
a practical embodiment, at least one coupling sub is
included in the drill string relatively close to the
drill bit. I.e., at least one coupling sub is included in
the downhole end of the drill string, or alternatively is
included in the bottomhole assembly (BHA).
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The BHA is the downhole portion of the drill string,
comprising (from the bottom up in a vertical well) the
bit, bit sub, a mud motor (in certain cases only), and
stabilizers. The bottomhole assembly provides a driller
with directional control of the well. The BHA may include
directional drilling and measuring equipment,
measurements-while-drilling tools, logging-while-drilling
tools and other specialized devices.
In an embodiment, the coupling sub can be controlled
from surface to change between the hinge mode and the
locking mode. The coupling sub may be provided with a
downhole control unit for controlling the locking means;
and signal means for providing a signal to the control
unit, wherein the control means are adapted to transfer
the locking means from the hinge position to the locking
position or vice versa in response to the signal provided
by the signal means.
Several possibilities exist for triggering the
movement of the locking sleeve for the purpose of
selecting a directional mode or a straight mode. For
instance, the signal means may comprise a pressure sensor
for sensing a pressure pulse pattern, a rotation sensor
for sensing a drill string rotation pattern or a strain
gauge for sensing a weight-on-bit pattern. According to
one of these possibilities, a pressure pulse pattern is
generated at surface which can be detected by the sensor
of the coupling sub. Alternatively, it is possible to
generate a drill string rotation pattern at surface for
detection by the signal means. In that case, the rotation
sensor is used. If the signal means include a load
sensor, such as a strain gauge, a weight-on-bit pattern
may be generated.
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Preferably, the signal means comprise a unit for
comparing directional data and/or formation evaluation
measurements with pre-programmed desired directional data
or formation characteristics.
According to another aspect, the invention provides a
directional drilling system including the coupling sub as
described above.
According to yet another aspect, the invention
provides a method for directional drilling of a borehole
in a formation along a predetermined trajectory, the
method comprising the steps of:
- providing a directional drilling system, comprising
a rotatable drill string comprising a first drill string
section and a second drill string section; a drill bit
connected to a downhole end of the drill string; and a
coupling sub comprising a first end connected to the
first drill string section; a second end connected to the
second drill string section; a hinge member between the
first end and the second end allowing hinging of the
second end relative to the first end; and locking means,
operable between a hinge mode and a locking mode for
locking the hinge member to prevent hinging of the second
end relative to the first end;
- operating the directional drilling system with the
locking means in the locking mode to drill a
substantially straight section of the trajectory; and
- operating the directional drilling system with the
locking means in the hinge mode to drill a curved section
of the trajectory.
Exemplary embodiments of the invention will be
described below with reference to the drawings, wherein:
Figure 1 shows a cross-section of a directional
drilling system according to the invention;
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Figure 2A shows a cross-section of an embodiment of a
coupling sub according to the invention in a locking
mode;
Figure 2B shows a cross-section of the embodiment of
Fig. 2A in a hinge mode;
Figure 3A shows a cross-section of another embodiment
of a coupling sub according to the invention in a locking
mode;
Figure 3B shows a cross-section of the embodiment of
Fig. 3A in a hinge mode;
Figure 4A shows a cross-section of yet another
embodiment of a coupling sub according to the invention
in a locking mode; and
Figure 4B shows a cross-section of the embodiment of
Fig. 4A in a hinge mode.
Figure 1 shows a directional drilling system 50
comprising a drill string 1 and an abrasive jet drill bit
2. The drill string 1 is connected to drive means 3 for
rotating the drill string. The drive means shown in Fig.
1 include a top drive, which is located at surface. Pump
4 and piping 5 may be coupled to the drive means 3, for
directing a drilling fluid and optionally abrasive
particles through an internal fluid passage of the drill
string 1 towards the drill bit 2. The drill bit 2 may be
provided with one or more jet nozzles 6 for discharging a
jet of drilling fluid and abrasive particles towards the
bottom 7 of the wellbore.
When drilling, a mixture of drilling fluid and
abrasive particles is pumped down the drill string 1 and
discharged from the nozzle 6. The discharged drilling
fluid is returned up the borehole 8 towards surface. The
drilling fluid may subsequently be returned to the pump
4. The abrasive particles may be returned as well.
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Alternatively, the abrasive particles may be re-
circulated downhole, for instance using a magnetic
recirculation system (not shown).
A coupling sub 9 may be accommodated in the drill
string 1. The coupling sub 9 can be transferred from a
stiff mode to a flexible mode and vice versa. In the
stiff mode, the whole of the drill string 1, the body sub
9 and the drill bit 2 are aligned, forming a stiff
longitudinal body for drilling a straight borehole. In
the flexible mode, the coupling sub allows the first end
thereof to hinge with respect to the opposite end. Thus,
the drill bit 2 can hinge with respect to the upper part
of the drill string 1. The flexible mode is most suitable
for drilling curved sections of the borehole.
Figure 2 shows a first drill string section 10 and a
second drill string section 11. Each of the drill string
sections are provided with a fluid channel 12, 13, which
are to be included in the internal fluid passage of the
drill string 1. The fluid channels 12, 13 are connected
by a flexible conduit 14. The drill string sections 10,
11 are connected by an outer coil 15 and an inner coil
16. The coils 15, 16 provide a predetermined flexibility
in bending of the first drill string section 10 relative
to the second drill string section 11. At the same time,
as a result of the opposite winding direction of the
coils 15, 16, the coils transfer torque from the first
drill string section to the second drill string section.
In other words, the springs 15, 16 allow axial hinging of
the first drill string section relative to the second
drill string section, but transmit rotary motion.
The first drill string section 10 is provided with a
locking sleeve 17 which is connected to an actuator 18.
The actuator can move the locking sleeve 17 in axial
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direction. The actuator includes for instance one or more
hydraulic cylinders provided with corresponding pistons
19. The pistons may be connected to extendable rods 20.
The rods 20 extend between the actuator 18 and the
locking sleeve 17. The rods 20 may extend through a bore
21 provided in an end of the first drill string section
10. An end of the locking sleeve facing the second drill
string section 11 may be shaped in the form of an
inverted cone 22. An end part 23 of the second drill
string section 11 may have a cone shape, corresponding to
the inverted cone 22.
Fig. 2A shows the locking means in the locking mode.
Herein, the pistons 19 are extended, pushing sleeve 17
forward wherein the inner surface 22 engages the
corresponding outer surface 23. The locking sleeve 17 may
be pressed against the locking surface 23 of the second
drill string section 11. Herein, the cones 22, 23 are
pushed against each other, preventing hinging of the
drill string sections 10, 11.
Figure 2B shows the locking sleeve 17 in the hinge
mode. Herein, the pistons 19 are retracted and the sleeve
17 is moved away from the second drill string section 11
along a distance L1. The retracted sleeve leaves a
clearance between the inner surface 22 of the sleeve 17
and the outer surface of the second drill string section
11. Due to the clearance, the drill string sections 10,
11 are able to axially hinge with respect to each other,
within the constraints posed by, for instance, the coil
springs 15, 16.
The level of flexibility allowed by the coupling sub
in the hinge mode (Fig. 2B) can be maximized to a
predetermined level. For instance, the distance L1 can be
limited so that the sleeve surface 22 will engage the
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locking surface 23 at a predetermined angle of hinging.
The maximum angle may for instance be in the order of 5
to 20 degrees. The distance Li may for instance be in
range of 1 to 5 inch (2.5 to 12.5 cm).
A flexible seal 24 may be arranged between the end of
the locking sleeve 17 and the second drill string part 11
and/or between the opposite end of the sleeve 17 and the
first drill string section 10. The seal 24 may prevent
the entry of unwanted materials, such as drill cuttings,
drilling fluid and the like, between the sleeve 17 and
the drill string sections 10, 11.
In the embodiment of Figure 3, the locking sleeve 17
has a smaller outer diameter. The smaller diameter
enables to apply a blocking ring 25. The blocking ring 25
has a cone shaped surface 26 corresponding to the surface
23 of the second drill string section 11. The blocking
ring prevents the entry of unwanted materials, such as
cuttings or abrasive particles. The flexible seal 24 may
be applied between the lower end of the blocking ring 25
and the second drill string section 11.
The embodiment of Fig. 3 functions similar to the
embodiment of Fig. 2. In the locking mode (Fig. 3A), the
actuator 18 pushes the sleeve 17 towards the second drill
string section. Herein, the inner surface 22 of the
sleeve 17 and the outer surface 23 of the second drill
string section 11 engage each other. In the hinge mode
(Fig. 3B), the actuator has moved the sleeve a
predetermined distance away from the second drill string
section 11, leaving a clearance between said locking
surfaces 22, 23.
In the embodiment of Figure 4, the first and second
drill string sections 10, 11 are connected using a
universal joint 27. Herein, a universal joint or
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universal coupling may also be referred to as a Cardan
joint. The universal joint is a coupling in a
substantially rigid pipe that allows the pipe to bend in
any direction, while being able to transmit rotary
motion. The universal joint may comprise a pair of hinges
located close together, oriented at 90 degrees to each
other. The hinges may be connected by a cross shaft.
The embodiment of Fig. 4 functions similar to the
embodiment of Fig. 2. The actuator 18 pushes the sleeve
17 towards the second drill string section 11. In the
locking mode (Fig. 4A), the inner surface 22 of the
sleeve 17 and the outer surface 23 of the second drill
string section 11 engage each other. In the hinge mode
(Fig. 4B), the actuator has moved the sleeve a
predetermined distance away from the second drill string
section 11, leaving a clearance between said locking
surfaces 22, 23.
The present invention is not limited to the above
described embodiments thereof, wherein many modifications
are conceivable within the scope of the appended claims.
For instance, features of respective embodiments may be
combined.
